In a manufacturing apparatus of a semiconductor, for example, physicochemical treatment is performed in a vacuum chamber. In this process a vacuum pressure regulating valve is employed for opening and closing a flow path connecting between the vacuum chamber and a vacuum pump that depressurizes the vacuum chamber and, normally, a vacuum pressure regulation system is constituted including a controller that gradually increases the aperture of the valve to prevent particles from being dispersed inside the vacuum chamber.
The vacuum pressure regulating valve includes, for example as disclosed in Patent Literature 1, Japanese Unexamined Patent Application Publication No. 2007-146908, a valve main body including, inside a valve housing in which a valve seat is provided in a flow path connecting between two main ports respectively connected to the vacuum chamber and the vacuum pump, a valve member configured to abut and separate from the valve seat so as to close and open the flow path, a valve shaft connected to the valve member and extending in the axial direction thereof out of the valve housing such that the distal end portion reaches a fluid pressure driving unit, and a return spring that biases the valve member in the direction to close the valve seat. The fluid pressure driving unit includes a pressure-receiving chamber configured to generate a pilot fluid pressure to be exerted on the valve member in the direction to open the flow path, including a pressure-receiving member attached to the distal end portion of the valve shaft, and connected to a pilot port for supplying and discharging the pilot fluid to and from the pressure-receiving chamber. The controller controls the position of the pressure-receiving member to adjust the aperture of the valve member, to thereby regulate the vacuum pressure in the vacuum chamber so as to slowly reduce the pressure.
With the vacuum pressure regulation system thus configured, however, a valve aperture preset in advance may fail to maintain the desired exhaust velocity in the case where abnormality such as leak in the vacuum chamber or other points in the vacuum system or clogging of a piping takes place, in which case the controller executes a feedback control so as to increase the valve aperture on the basis of comparison between an output of a pressure sensor that detects the pressure in the vacuum chamber and a signal of a control command such as an externally specified pressure or transition of the exhaust velocity. Nevertheless, the pressure in the vacuum chamber is unable to be lowered while the abnormality remains unremoved, and therefore the valve is finally set to the maximum aperture by the feedback control, still failing to attain the desired exhaust velocity. The abnormality is unable to be detected at an early stage unless the controller is provided with an abnormality detection device. If the vacuum pump continues to aspirate gas of a high temperature from the vacuum chamber while the vacuum pressure regulating valve remains fully opened, the piping may be damaged and even the vacuum pump may be broken down, in which case an enormous cost and time is required for restoring the system.
To avoid the foregoing problem, the vacuum pressure control system according to Patent Literature 2, Japanese Unexamined Patent Application Publication No. 2006-18767, is configured to decide that abnormality has occurred in the case where an output of a pressure sensor provided in a vacuum container is larger than a predetermined value when the valve is set to a predetermined aperture, thus to detect the abnormality of the system at an early stage.
However, the decision of the abnormality made by the vacuum pressure control system according to Patent Literature 2 is with respect to a pinpoint in the transition of the valve aperture, and does not lead to the conclusion whether the evacuation is being normally and continuously performed. Moreover, the pinpoint aperture and setting of a pressure correlated thereto involve various experimental factors, and therefore it is difficult to set an appropriate value through a simple process, and further the transition of the aperture with time is unable to be ascertained.